Constrained layer dampers (CLDs) are known for their excellent damping characteristics and have found wide use throughout various industries. In the automotive industry, for example, constrained layer dampers are arranged about a vehicle passenger compartment for abating engine and outside noises and for deadening resonant vibrations experienced by the driver and passenger. The constrained layer dampers may be affixed to or incorporated into panels surrounding the passenger compartment. For example, the constrained layer dampers may be affixed to or incorporated into a vehicle dashboard and the wheel housing. Constrained layer dampers also may be placed in various panels, such as the door, roof, and floor about the passenger compartment.
The performance and effectiveness of the constrained layer dampers around the vehicle passenger compartment can greatly improve the tranquility of the driving experience by isolating the driver and other compartment occupants from outside disturbances. The quietness and smoothness are of significant value to many consumers, and are often considered by professional and consumer reviewers of the vehicle in grading the vehicle. Consequently, the constrained layer dampers may significantly influence the sales and profitability of a vehicle.
Applications for constrained layer dampers are not restricted to the automobile industry. Constrained layer dampers also are incorporated into industrial and residential machinery, business and computer equipment, household appliances, power tools, and other devices requiring noise and/or resonance vibration reduction. As with automobiles, the effectiveness of constrained layer dampers in each application strongly influences consumer enjoyment and sales.
Due to the relatively high temperature environments in which constrained layer dampers are often used, situations arise in which it is desirable for the CLDs to exhibit a peak damping temperature well in excess of room temperature. For example, heat generated by the engine of a vehicle or machinery may reach temperatures of about 80° C. to about 90° C., and even higher in some instances. While viscoelastic materials used in known constrained layer dampers may exhibit high peak damping temperatures such materials do not possess strong pressure sensitive adhesive characteristics at room temperature. As the result of poor pressure sensitive adhesive characteristics, fixedly securing the constrained layer damper to a substrate, such as an automobile part, may prove difficult or require expensive process equipment and procedures. The application operation by which the constrained layer damper is secured to the substrate often is performed in a heated environment, such as in an oven or a hot press. Such constrained layer dampers lack the versatility to be applied and adequately secured to a substrate in room temperature environments.
Viscoelastic layers made of silicone pressure sensitive adhesives can provide desired high temperature (e.g., about 80-90° C.) damping characteristics while also retaining room temperature pressure-sensitive adhesion characteristics. However, when applied to certain surfaces, such as a rough surface as often found on a cast aluminum engine cover, the silicone viscoelastic layer in a CLD must possess a relatively large thickness for proper bonding. Thin silicone layers may not wet out adequately, resulting in poor adhesion. On the other hand, increasing the thickness of a silicone viscoelastic layer can adversely affect the constrained layer damper performance by reducing peak damping temperature of the damper below the operating temperature experienced by the damper in use. Additionally, because silicone is relatively expensive compared to other damping materials, thick viscoelastic layers are economically undesirable.